The present embodiment relates generally to a composition for sealing a subterranean zone penetrated by a well bore.
In the drilling and completion of an oil or gas well, a composition is often introduced in the well bore for cementing casing or pipe strings. In this process, known as xe2x80x9cprimary cementing,xe2x80x9d a composition is pumped into the annular space between the walls of the well bore and the pipe string. The composition sets in the annular space, supporting and positioning the pipe string, and forming a substantially impermeable barrier which divides the well bore into subterranean zones. After primary cementing, the undesirable migration of fluids between zones is prevented. Likewise, compositions are often subsequently introduced into a subterranean zone for remedial operations to recover circulation or to plug the well bore. Most remedial operations comprise introducing a composition into the well bore to reestablish a seal between the zones.
Previously, a variety of cement compositions have been used for cementing. However, cement is undesirable for use with expandable casing. After the expandable casing is placed down hole, a mandrel is run through the casing to expand the casing, and expansions up to twenty five percent are possible. As cement is incompressible, expansion of the casing can lead to crushing of the cement, and consequent loss of effectiveness regarding the zones. Therefore, a composition with comparable strength to cement, but greater elasticity and compressibility is required for cementing expandable casing.
A sealing composition according to the present embodiment basically comprises a mixture of latex, dithio carbamate, zinc oxide, and sulfur, for sealing a subterranean zone penetrated by a well bore. The sulfur containing component vulcanizes the latex to form a solid mass which seals the zone.
In a first embodiment, the composition comprises a mixture of latex, dithio carbamate, zinc oxide, and sulfur. Preferably, the amount of latex is maintained at a 41-90 percent ratio by weight of the composition. The dithio carbamate is preferably present in an amount that is 0.1-2 percent of the latex by weight. The zinc oxide is preferably present in an amount that is 2-5 percent of the latex by weight. The sulfur is preferably present in an amount that is 1-4 percent of the latex by weight.
The composition may further comprise stearic acid. The stearic acid is preferably present in an amount that is 0.1-2 percent of the latex by weight.
The composition may further comprise a weighting agent. The weighting agent is preferably present in an amount that is 0.1-150 percent of the latex by weight.
The composition may further comprise acetylenic alcohol for defoaming, such as is available from Halliburton Energy Services of Duncan, Okla., under the trademark xe2x80x9cD-AIR3(trademark).xe2x80x9d The acetylenic alcohol is preferably present in an amount that is 0.001-0.2 percent of the latex by weight.
In a second embodiment, the composition comprises a mixture of latex, dithio carbamate, zinc oxide, sulfur, and a foaming agent, wherein the mixture is foamed. Preferably, the amount of latex is maintained at a 41-90 percent ratio by weight of the composition. The dithio carbamate is preferably present in an amount that is 0.1-2 percent of the latex by weight. The zinc oxide is preferably present in an amount that is 2-5 percent of the latex by weight. The sulfur is preferably present in an amount that is 12 percent of the latex by weight. The foaming agent is preferably present in an amount that is 2-4 percent of the latex by weight.
The composition may further comprise stearic acid. The stearic acid is preferably present in an amount that is 0.1-2 percent of the latex by weight.
The composition may further comprise a weighting agent. The weighting agent is preferably present in an amount that is 0.1-150 percent of the latex by weight.
As will be understood by those skilled in the art, the latex for either embodiment may be any of a variety of well known rubber materials commercially available which contain unsaturation in the backbone of the polymer. These include natural rubber (cis-1,4-polyisoprene), modified types thereof, synthetic polymers, and blends of the foregoing. The synthetic polymers include styrene/butadiene rubber, cis-1,4-polybutadiene, neoprene rubber, acrylonitrile styrene/butadiene rubber, and cis-1,4-polyisoprenerubber.
For either embodiment, the composition preferably includes a latex comprising a styrene/butadiene copolymer latex emulsion prepared by emulsion polymerization. The weight ratio of styrene to butadiene in the latex can range from 10:90 to 90:10. The emulsion is a colloidal dispersion of the copolymer. The colloidal dispersion includes water from about 40-70% by weight of the emulsion. In addition to the dispersed copolymer, the latex often includes small quantities of an emulsifier, polymerization catalysts, chain modifying agents and the like. Also, styrene/butadiene latexes are often commercially produced as terpolymer latexes which include up to about 3% by weight of a third monomer to assist in stabilizing the latex emulsions. Non-ionic groups which exhibit stearic effects and which contain long ethoxylate or hydrocarbon tails can also be present.
Most preferably for either embodiments, the composition includes a latex with a styrene/butadiene weight ratio of about 25:75, with the styrene/butadiene copolymer suspended in a 50% by weight aqueous emulsion, available from Halliburton Energy Services of Duncan, Okla., under the trademark xe2x80x9cLATEX 2000(trademark).xe2x80x9d
The weighting agent for either embodiment may be silica flour, such as is available from Halliburton Energy Services of Duncan, Okla., under the trademark xe2x80x9cSSA-1(trademark).xe2x80x9d Alternatively, the weighting agent may be manganese oxide weighting additive, available from Halliburton Energy Services of Duncan, Okla., under the trademark xe2x80x9cMICROMAX(trademark).xe2x80x9dAlternatively, the weighting agent may be crystalline silica with an average particle size of 10 microns, available from Halliburton Energy Services of Duncan, Okla., under the trademark xe2x80x9cMICROSAND(trademark).xe2x80x9d
Dithio carbamate for either embodiment is available from Halliburton Energy Services of Duncan, under the trademark xe2x80x9cFLEXCEM COMPONENT L(trademark).xe2x80x9d
The foaming agent for the second embodiment may be an ethoxylated alcohol ether sulfate surfactant, which is available from Halliburton Energy Services of Duncan, under the trademark xe2x80x9cZONE SEAL 2000 (trademark).xe2x80x9d The ZONE SEAL 2000 surfactant is the subject of U.S. Pat. No. 6,063,738, the entire disclosure of which is incorporated herein as if reproduced in its entirety. Alternatively, the foaming agent may be an amidopropylbetaine surfactant, which is available from Halliburton Energy Services of Duncan, under the trademark xe2x80x9cHC-2(trademark).xe2x80x9d The HC-2(trademark) surfactant is discussed in U.S. Pat. No. 5,588,489, the entire disclosure of which is incorporated herein as if reproduced in its entirety.
The following examples are illustrative of the methods and compositions discussed above.